EP3019294B1 - Method for working a running surface of a cylinder of an internal combustion engine - Google Patents

Description

The invention relates to a method for machining a running surface of a cylinder of an internal combustion engine. In particular, the invention relates to a method for coating the tread, which is previously roughened in order to improve the adhesion of the coating.

For reasons of weight, internal combustion engines in motor vehicles are usually designed with a cylinder crankcase made of light metal, in particular aluminum. The problem with this, however, is that the inner walls of the cylinders formed by the cylinder crankcase are only inadequately suitable as running surfaces for the pistons because of the tribological properties of the light metal, in particular the comparatively poor wear resistance.

To avoid this problem, many internal combustion engines with a cylinder crankcase made of light metal use cylinder liners made of e.g. gray cast iron, whereby the advantages of light metal (low specific weight) can be combined with those of gray cast iron (good tribological properties).

As an alternative to this, it is known to provide the running surfaces of the light metal cylinder crankcase with a coating in order to achieve the desired tribological properties for the running surfaces. The coating is regularly implemented by melting the coating material and spraying it onto the cylinder walls.

When coating cylinder walls, it is of particular importance to achieve good adhesion of the coating to the base material. For this purpose, it is known to roughen the running surfaces of the cylinder crankcase before coating in order to increase the contact area between the layers. In many cases, attempts are also made to form undercuts in the roughened running surface, into which the melted material of the coating can penetrate, in order to realize a form-fitting connection between the layers after hardening.

A known possibility for roughening the cylinder walls is the cutting or non-cutting introduction of grooves or grooves.

So it is, for example, from the DE 10 2009 027 200 B3 known to introduce a spiral groove with a particularly rectangular or trapezoidal cross-section in the cylinder wall in a first process step for roughening a cylinder wall. This can be done either by cutting or without cutting. In a second step, sections of the web running spirally between the groove are then plastically deformed radially in order to form undercuts. To make the groove, a tool is used which has a single cutting edge, the tool being driven both in rotation and being moved axially along the longitudinal axis of the cylinder.

A similar procedure is from the EP 2 112 359 A1 known. It is also disclosed there that, instead of a spiral groove, a multiplicity of grooves running in the circumferential direction can be made in the cylinder wall.

From the DE 10 2012 214566 A1 discloses a method of preparing a surface for mechanically attaching a spray coating to a surface. A first series of grooves formed in the surface are intersected by a second series of grooves formed in the surface. Several peaks are formed at the intersections. The spray coating is mechanically attached to the tips protruding over the first row of grooves. The surface includes the first series of grooves and the second series of grooves that intersect the first series of grooves. The second row of grooves forms an undercut section, or point, at the intersection of the grooves, which mechanically anchors the spray coating. The method of this document thus comprises the features of the preamble of independent claim 1.

EP 1 868 054 A1 discloses milling circumferential grooves in a cylindrical bore, a disk-shaped cutting tool rotating about its longitudinal axis and at the same time being moved on an annular path.

Also from the U.S. 2,949,064 A it is known to mill circumferential grooves in a cylindrical bore while a disk-shaped cutting tool rotates about its longitudinal axis and is moved at the same time on an annular path.

From the DE 10 2010 054392 A1 a cutting tool for machining a workpiece is known. The tool has saw blades arranged in parallel for producing grooves.

Also from the DE 10 2011 055210 A1 a cutting tool for machining a workpiece is known which has saw blades arranged in parallel for producing grooves.

Disadvantages of the known methods are the considerable time required to make the grooves and the comparatively short downtimes for them Proceeding from this prior art, the invention was based on the object of further improving the economic efficiency of coating cylinder walls of internal combustion engines.

This object is achieved by a method according to independent patent claim 1. Advantageous embodiments of the method according to the invention are the subject matter of the dependent claims and emerge from the following description of the invention.

A generic method for machining a wall of a cylinder (cylinder wall) of an internal combustion engine, in which circumferential grooves are machined into the cylinder wall, is further developed according to the invention in that at least one ring-shaped (preferably circular) saw blade is used to make the grooves, which is attached to its The circumference is provided with a plurality of cutting teeth, the saw blade rotating around its longitudinal axis and moving on an annular path (around the longitudinal axis of the cylinder) in order to make one of the grooves in the cylinder wall.

The saw blade or blades are moved on an annular path that is not circular but, for example, star-shaped or otherwise non-uniform. This creates a variation in the groove depth which, due to the lack of rotational symmetry of the groove base course, can effectively prevent the coating on the cylinder wall from twisting.

The term "cutting teeth" should be understood to mean any cutting elements that realize the material removal by machining, which do not necessarily have to be formed in one piece with a base body of the saw blade and also do not necessarily have to be rotationally symmetrical and / or evenly spaced on the circumference of the base body.

By using a large number of cutting teeth in connection with the two overlapping movements of the annular saw blade for insertion Each of the grooves can significantly increase the service life of the tool compared to the known methods in which only a single cutting edge or a few cutting edges that then work out different grooves are used.

The roughening of the cylinder wall according to the invention can in particular serve to achieve good adhesion of a coating layer which is subsequently applied to the cylinder wall and which serves as the running surface of the cylinder. The method according to the invention can accordingly include coating the cylinder wall in a subsequent method step. This coating can be carried out in any manner known in the prior art, whereby a thermal spraying process, in which the coating material is sprayed onto the cylinder wall in the melted state and cures there, can be used. Examples of thermal spray processes are wire arc spraying and plasma coating.

In order to further improve the adhesion of the coating to the cylinder wall, it can preferably be provided that the webs formed between the grooves are reshaped prior to coating in such a way that they form undercuts (with respect to the radial direction, starting from the longitudinal axis of the cylinder). This results in an interlocking of the coating layer in the roughened cylinder wall, which is equivalent to a form-fitting connection. In addition, the plastic deformation of the webs can achieve a compression of the material in the webs, which can again benefit an improvement in the adhesion between the coating and the cylinder wall. The webs can be deformed symmetrically and / or asymmetrically with respect to the vertical axes of the webs (running radially to the longitudinal axis of the cylinder). The webs can preferably be reshaped by means of a roller burnishing tool. In particular, to produce asymmetrically deformed webs, it can be provided to use a roller burnishing tool which has a plurality of extendable and retractable rollers over the circumference and / or along its length, which are extended and retracted accordingly during the roller burnishing process.

In an advantageous embodiment of the method according to the invention, it can be provided that the width of the saw teeth corresponds to the intended groove width. It can thereby be achieved that the completion of a groove can take place in just one circular path movement of a saw blade. Axial movement of the saw blade (i.e. in the direction of the longitudinal axis of the cylinder) when creating the individual grooves can thus be avoided. However, it can also be provided that the width of all or individual grooves is greater than that of the saw teeth or the saw blade. In particular, it can also be provided that the groove widths vary in the case of a large number of grooves. This can also be provided in order, for example, to vary the widths of the webs formed between adjacent grooves with the same center distance between the individual grooves. For example, it can be provided that the web widths in a central section of the cylinder (in relation to the longitudinal axis) are narrower than in one or preferably both end sections. As a result, it can be achieved that in the central section particularly stressed by the piston during later operation of the internal combustion engine, particularly good adhesion of the coating to the cylinder wall is achieved, while in the end-side sections adequate adhesion is achieved with reduced processing effort.

It is also possible to achieve varying web widths with constant groove widths by changing the center distances of the grooves over the length of the cylinder. Here, too, it can be provided that the web widths in a central section of the cylinder (in relation to the longitudinal axis) are narrower than at one or preferably both end sections. Of course, varying center distances and varying groove widths can also be combined with one another.

In order to shorten the processing time for the cylinder and to lengthen the service life of the device used for this purpose, a particularly preferred embodiment of the method according to the invention can provide for a large number (e.g. 5 to 100) of saw blades arranged in parallel to be used, which are cut by the (preferably synchronously running) inventive superposition of two rotary movements each have a groove in the Insert cylinder wall. As a result, all the grooves provided can possibly be made in the cylinder wall in just one pass (ie in a circular path movement of a tool carrying the saw blades).

However, it can be advantageous to select the distance between the grooves and thus the width of the webs formed between adjacent grooves to be very small (e.g. approx. 0.15 mm to 0.3 mm). In this case, the production of a tool which has a number of saw blades corresponding to the number of grooves provided can only be produced with great effort or not with the required durability. This problem can advantageously be avoided by using a tool whose number of saw blades is smaller (and in particular corresponds to an integer fraction, ie half, a third, a quarter, etc.), the distance between adjacent saw blades being one such a tool is a multiple of the intended width (in the final state of the running surface, ie after all the grooves provided have been introduced) of the webs formed between the grooves. The distance x between the saw blades is sensibly calculated as follows: x = n * y + (n-1) * z, where n is an integer, y is the intended web width and z is the intended groove width. In this case, n can in particular correspond to the number of passages which are provided for introducing all the grooves.

To make the grooves, a number of grooves corresponding to the number of saw blades can thus be made in the cylinder wall in a first pass. The saw blades (in particular a tool carrying the saw blades) can then be moved in the axial direction in the cylinder by a distance that corresponds to the sum of the intended groove width and the intended web width in order to again introduce a corresponding number of grooves, each between two previously introduced grooves are arranged. This can be continued until the intended number of grooves has been made.

In addition to the preferred embodiment, in which the grooves are introduced into the cylinder wall with essentially identical spacing, it can also be provided that the spacings between the grooves and thus the widths of the Bars vary.

The effect of the method according to the invention can advantageously be further enhanced by making the grooves in at least two passages, the non-circular ring paths in which the saw blade moves in the individual passages are not identical. The non-circular ring tracks can be fundamentally different and / or rotatably offset from one another by less or more than 360 °.

As an alternative or in addition to this, twisting of the coating can also be avoided in that at least one of the grooves is not or not completely circumferential. For example, at least one of the grooves can be interrupted at at least one point. Some of several grooves can also run in a spiral. At least one groove extending in the longitudinal direction of the cylinder can also be provided.

In a further preferred embodiment of the method according to the invention it can be provided that one or more saw blades are used in which the tips of at least some of the cutting teeth are beveled or rounded laterally (i.e. in the transition to the side surfaces). In this way, a correspondingly rounded or beveled transition of the side walls of the grooves into the groove bases can be achieved. Such a transition can be particularly advantageous if the webs are reshaped before the coating, since this allows the maximum stress to be reduced during the reshaping. A tearing of the cylinder wall in the transitions can thus be effectively prevented.

Fig. 1:

das Einbringen von Nuten in eine Zylinderwand als ein erster Schritt eines nicht erfindungsgemäßen Verfahrens zum Beschichten der Zylinderwand;

Fig. 2:

eine Draufsicht auf einen Teil des für die Durchführung des Verfahrens gemäß Fig. 1 eingesetzten Systems aus Zylinderkurbelgehäuse und Werkzeug;

Fig. 3:

eine mit dem erfindungsgemäßen Verfahren erzeugte Ringbahnform, auf der das Werkzeug bewegt werden kann, sowie der sich daraus Verlauf der Nutgründe;

Fig. 4:

eine alternative Möglichkeit zum Einbringen der Nuten in die Zylinderwand;

Fig. 5:

ein Rollieren des zuvor mit den Nuten versehenen Zylinders als ein zweiter Schritt des Verfahrens zum Beschichten der Zylinderwand;

Fig. 6:

die Umformung der zwischen den Nuten ausgebildeten Stege als Ergebnis des Rollierens bei einer ersten Querschnittsform der Nuten;

Fig. 7:

die Umformung der zwischen den Nuten ausgebildeten Stege als Ergebnis des Rollierens bei einer zweiten Querschnittsform der Nuten;

Fig. 8:

ein Aufbringen einer Beschichtungsschicht auf die zuvor bearbeitete Zylinderwand als ein dritter Schritt des Verfahrens zum Beschichten der Zylinderwand;

Fig. 9:

eine gleichgerichtete asymmetrische Umformung der zwischen den Nuten ausgebildeten Stege; und

Fig. 10:

eine gegenläufige asymmetrische Umformung der zwischen den Nuten ausgebildeten Stege.

The invention is explained in more detail below with reference to an exemplary embodiment shown in the drawings. The drawings show in:

Fig. 1:

the making of grooves in a cylinder wall as a first step of a method not according to the invention for coating the cylinder wall;

Fig. 2:

a plan view of part of the for carrying out the method according to Fig. 1 used system consisting of cylinder crankcase and tool;

Fig. 3:

an annular track shape produced with the method according to the invention, on which the tool can be moved, and the course of the groove bases resulting therefrom;

Fig. 4:

an alternative way of making the grooves in the cylinder wall;

Fig. 5:

roller burnishing the previously grooved cylinder as a second step of the method for coating the cylinder wall;

Fig. 6:

the deformation of the webs formed between the grooves as a result of rolling in a first cross-sectional shape of the grooves;

Fig. 7:

the deformation of the ridges formed between the grooves as a result of rolling in a second cross-sectional shape of the grooves;

Fig. 8:

applying a coating layer to the previously processed cylinder wall as a third step of the method for coating the cylinder wall;

Fig. 9:

rectified asymmetrical deformation of the webs formed between the grooves; and

Fig. 10:

a counter-rotating asymmetrical deformation of the webs formed between the grooves.

The Figures 1 to 8 show, in schematic representations, various steps of a method for coating a wall of a cylinder 2 formed by a cylinder crankcase 1 and details of the devices used.

In a first step of a method not according to the invention, the Cylinder wall a plurality of circumferential, parallel grooves 3 introduced by machining. For this purpose, a tool is used which comprises one or more circular saw blades 4 which are fastened to a tool carrier 5. The saw blades include a large number of cutting teeth 6 on the circumferential side.

The Fig. 1 shows one possibility of making all the grooves 3 by means of a single saw blade 4. This is driven to rotate about its own longitudinal axis 7, dipped into the cylinder 2 until the desired position for the first groove 3 to be made is reached, and then radially (or at least with a radial movement component) in the direction of the cylinder wall. The saw blade 4 cuts into the cylinder wall to the desired groove depth.

The saw blade 4 is then, for example, on a circular path 8 (cf. Fig. 2 ) moved about the longitudinal axis 9 of the cylinder 2, whereby the first groove 3 is made with a constant groove depth in the cylinder wall. The saw blade 4 is then moved radially onto the longitudinal axis 9 of the cylinder 2 in order to move it out of the first groove 3. By moving the tool in the direction of the longitudinal axis of the cylinder 2, the saw blade 4 is then positioned at a point which is provided for the introduction of a second groove 3. In a manner corresponding to that of the first groove 3, the second groove 3 is then made in the cylinder wall. By moving the tool step-by-step along the longitudinal axis 9 of the cylinder, all the grooves 3 provided can be made in the cylinder wall (cf. Fig. 5 ).

The Fig. 4 shows an alternative procedure for making the grooves 3 in the cylinder wall. A tool is used there that comprises several saw blades 4 arranged parallel and coaxially with respect to their longitudinal axis. The number of saw blades 4 is less than the intended number of grooves 3 and is in particular 1 / n (n: whole number) of the intended number of grooves 3. Furthermore, the distance between adjacent saw blades 4 is greater than the intended distance between adjacent grooves (after all grooves have been made). Specifically, the sum of (n-1) is multiplied by the groove width and n is multiplied by the intended width of the webs 10 formed between adjacent grooves 3 as the distance between the Saw blades 4 provided.

In a first pass, by moving the tool as in the method according to FIG Fig. 1 a number of grooves 3 corresponding to the number of saw blades 4 can be made in the cylinder wall. The tool is then moved in the direction of the longitudinal axis 9 of the cylinder 2 by a distance that corresponds to the intended web width and the groove width and then, in a second pass, a corresponding number of grooves 3 are made in the cylinder wall. The machining process is repeated a total of n times until all the grooves 3 provided have been made.

If the tool is moved in a circular path 8 around the longitudinal axis 9 of the cylinder 2, the result is a rotational symmetry of the introduced grooves 3 and consequently the outside of a coating layer 11 subsequently applied to the cylinder wall can be prevented by the material connection between the coating layer 11 and the cylinder wall. Should this prove to be insufficient, twisting of the coating layer can be prevented in that, according to the invention, the tool is not moved on a circular path 8 but in a non-uniform ring path 12 around the longitudinal axis 9 of the cylinder 2. In the Fig. 3 this is shown for a star-shaped ring track 12, for example. The saw blade (s) 4 accordingly plunge into the cylinder wall at different depths in sections in one cycle, resulting in a correspondingly non-uniform course of the groove base or bases.

The safeguard against rotation can be improved even further if the ring tracks 12, which are traversed by the saw blade 4 or the saw blades 4 in the individual passages, are rotationally offset, as is also the case in FIG Fig. 3 is shown. There, the course of the ring track and the resulting course of the groove bases are shown in solid lines for a first pass and in dashed lines for a second pass.

After all the grooves 3 have been made in the cylinder wall, the to plastically reshape webs 10 formed between adjacent grooves 3 in order to form undercuts or constrictions of the groove cross-sections, which ensure a form-fitting fixation of the subsequently applied coating layer 11 on the cylinder wall. For reshaping, a roller burnishing tool 13 is used that has a plurality of roller burnishing bodies 14 which are arranged on the circumferential side in depressions of a base body 15 and project beyond the outside of the base body 15 in the radial direction. The rotating roller burnishing tool 13 is moved along the longitudinal axis 9 of the cylinder 2, the forming of the webs 10 being realized in that the (largest) circumference formed by the burnishing bodies 14 is larger in diameter than the inner diameter of the cylinder 2 formed by the webs 10 is. The roller burnishing tool 13 can be immersed in the cylinder 2 by a slightly conical configuration of the roller burnishing bodies 14.

In the Figures 6 and 7 the change in the cross-sectional shape of both the webs 10 and the grooves 3 that can be achieved by roller burnishing can be seen schematically. In the initial state, webs 10 and grooves 3 that are essentially rectangular are given trapezoidal cross-sections, the width of the grooves 3 being greater on the opening side than in the groove base.

For those in the Fig. 6 The rectangular starting cross-sectional shapes shown here can occur during forming in the right-angled transitions from the side surfaces of the grooves 3 to the groove bottoms, which can lead to local tearing of the material of the cylinder crankcase 1. These stress peaks can be avoided or reduced if the transition from the side surfaces to the groove bottoms is less acute, e.g. by means of angled (cf. Fig. 7 ) or rounded transitions. Such transitions can be achieved by appropriately shaping the cutting teeth 6 of the saw blades 4.

In addition to the Figures 6 and 7 Symmetrical deformation of the webs shown, asymmetrical deformation is also possible, as is the case, for example, in FIG Figures 9 and 10 is shown. The oppositely asymmetrical deformation according to the Fig. 10 thanks to a particularly good connection between the Mark the coating layer with the cylinder wall.

For the formation of sufficiently large undercuts during forming, a ratio of the web width to the groove depth of approximately 1 to 1 can be advantageous. The web width can be 0.15 mm to 0.3 mm and the groove depth 0.1 mm to 0.4 mm, for example (before the deformation in each case).

After the webs 10 have been reshaped, the coating layer 11 is applied to the cylinder wall (cf. Fig. 8 ). This serves as a running surface for a piston of the internal combustion engine that is guided in the cylinder. The coating can in particular be applied by means of thermal spraying (for example arc wire spraying), for which a spray head 16 is driven in rotation in a known manner and is moved along the longitudinal axis 9 of the cylinder 2. The melted coating material can penetrate into the grooves 3, fill them and - after hardening - form the desired form-fitting connection with the cylinder wall.

If the cylinder crankcase 1 forms more than one cylinder 2, it can be provided to machine several and in particular all cylinders 2 according to the invention at the same time.

Claims (10)

1. Method for machining a wall of a cylinder (2) of an internal combustion engine, with circumferential grooves (3) being machined into the wall, characterized in that at least one annular saw blade (4) which is provided with a large number of cutting teeth (6) on its circumference is used to make the grooves (3), the saw blade (4) being moved so as to rotate about its longitudinal axis (7) and being moved on an annular path (12), the annular path (12) not being circular.
2. Method according to claim 1, characterized in that the width of the cutting teeth (6) corresponds to the intended width of the grooves (3).
3. Method according to either claim 1 or 2, characterized in that a large number of saw blades (4) arranged in parallel are used.
4. Method according to claim 3, characterized in that the distance between adjacent saw blades (4) is a multiple of the width of lands (10) formed between the grooves (3) in the final state of the wall.
5. Method according to any of the preceding claims, characterized in that the grooves (3) are made in at least two passes, the non-circular annular paths (12) in which the saw blade (4) moves in the two passes not being identical.
6. Method according to any of the preceding claims, characterized in that the annular path (12) is star-shaped.
7. Method according to any of the preceding claims, characterized in that the cutting teeth (6) are laterally beveled or rounded.
8. Method according to any of the preceding claims, characterized in that the lands (10) formed between the grooves (3) are reshaped in order to form undercuts.
9. Method according to claim 8, characterized in that the lands (10) are reshaped by means of roller burnishing.
10. Method according to any of the preceding claims, characterized in that the wall is then coated.

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